MUSCLES-EXTERNAL ROTATORS OF THE HIP

SUMMARY

1. PIRIFORMIS - arises from the middle 3 pieces of the sacrum, passes laterally behind the sacral plexus, to emerge through the greater sciatic foramen. It inserts into the apex of the greater trochanter. Supplied by the nerve to the piriformis (S1 + S2, anterior rami).

2. SUPERIOR GEMELLUS - arises from the ischial spine. Supplied by nerve to the obturator internus. 

3. OBTURATOR INTERNUS - arises from the pelvic surface of the obturator membrane + surrounding bone. Passes through the lesser sciatic foramen, makes a right-angled turn around the lesser sciatic notch. Together with the superior and inferior gamelli (forming the tricipital tendon) it is inserted into the medial surface of the greater trochanter. Supplied by nerve to the obturator internus. 

4. INFERIOR GAMELLUS - arises from the ischeal tuberosity (at the margin of the lesser sciatic notch). Supplied by nerve to the obturator internus. 

5. QUADRATUS FEMORIS - rectangular muscle that arises from the ischeal tuberosity, below the attachment of the INFERIOR GEMELLUS. Passes laterally to be inserted into the quadrate tubercle (formed by the fusion of the epiphysis of the greater trochanter) on the intertrochanteric crest of the femur+ lesser trochanter. Supplied by the nerve to the quadratus femoris.

6. OBTURATOR EXTERNUS - arises from the obturator membrane + anterior bony margin of obturator foramen; passes laterally and posteriorly beneath the neck of the femur to be inserted into the trochanteric fossa. Supplied by the posterior division of the obturator nerve. Action - stabilizes hip joint + external rotator of femur.

Reference(s)

R.M.H McMinn (1998). Last’s anatomy: regional and applied. Edinburgh: Churchill Livingstone.
Gray, H., Carter, H.V. and Davidson, G. (2017). Gray’s anatomy. London: Arcturus.